The invention relates to a method for producing a rail substructure for railroad tracks, for which a rail bed is concreted and dowels are used to anchor the rails positively in the concrete.
For conventional railroad tracks, the substructure generally consists of a bed of road metal and railroad ties of wood or concrete, to which fastening claws are attached with bolts, so that the rails can be fastened adjustably. If the railroad ties are fabricated parts made from concrete, the dowels, into which the bolts are screwed later on, are cast in the finished concrete parts already during the manufacture of the railroad ties. The dowels can thus be anchored reliably in the concrete.
Rail substructures are also already known, for which a rail bed of concrete is provided instead of a bed of road metal. In the case of a known method for producing such a rail substructure, a rail bed is concreted with a flat surface in a first concreting step. When the concrete has set, the pre-fabricated railroad ties are placed upon it. These railroad ties are then concreted in a second step in a further layer of concrete. However, this method is time-consuming and costly.
It is an object of the invention to indicate a method of the type named above, which makes it possible to produce rail substructure more easily, more quickly and less expensively.
Pursuant to the invention, this objective is accomplished owing to the fact that, when concreting the rail bed, the dowels are inserted in the concrete, while the latter is still deformable.
This method has the advantage that pre-fabricated railroad ties are no longer required and that the rail substructure can be produced rationally in a single concreting step.
In the simplest case, the positive anchoring of the dowels in the concrete can be achieved owing to the fact that the dowels, which are provided with outwardly protruding projections, are simply pressed from above into the soft concrete. Since the concrete is still somewhat flowable, it flows around all the projections, so that the desired positive connection is brought about. In order to increase the reliability of this method, it is possible, after the dowels have been inserted, to consolidate the concrete with the help of a shaker or the like, the dowels being held in position during the shaking preferably with the help of an inserted mandrel. Moreover, it is possible to carry out the consolidation process so that, at the same time, railroad tie-like elevations are formed in the surface of the track bed at the same time, either in the form of continuous railroad ties for both rails or in the form of two isolated islands, on which in each case a single rail is to be fastened. At the same time, this method has the advantage that, during the consolidation process, there is flow of material in the still deformable concrete in the direction of the islands and, with that, in the direction of the dowels, so that the flow of concrete around the dowels is supported.
Another possibility for ensuring a reliable positive connection between the dowels and the concrete consists therein that the dowels are formed as straddling dowels, which initially are pressed into the concrete in the unexpanded state and expanded only then, so that they are set positively into the surrounding concrete. Since the expansion of the dowels at the same time leads to a consolidation of the surrounding concrete, reliable anchoring of the dowels can be achieved.
Pursuant to a further variation of the method, which is regarded as particularly preferred at the present time, the dowels are provided with thread-like projections on their peripheral surface and, as they are lowered into the concrete, are caused to rotate, so that they are screwed into the concrete. In this way, it can be achieved that the spaces between the projections are filled with concrete from the very start and, with that, a reliable indenting of the dowels in the concrete is achieved.
A dowel for implementing this variation of the method is also an object of the invention.
Preferably, an internal thread, into which later on the bolt for fastening the rail foot claw can be screwed, is prepared in the dowel. So that this thread (machine thread) does not become contaminated prematurely with concrete, the dowel preferably has a closing mechanism for temporarily closing the upper opening of the dowel. This closing mechanism can be formed by an inserted or slipped-on cap, a slider, by soft lips or by closing elements with break-off sites, which are gated to the dowel.